This invention relates generally to wind electric plants, and more particularly to a wind electric plant of the type which includes a wind-driven propeller or the like connected to drive an alternator for producing electrical energy.
In prior art wind electric plants of the type noted above, the field windings of the alternator are excited by means of an exciter generator provided on the tower of the wind electric plant adjacent the alternator thereof. Accordingly, both the alternator and the exciter generator are supported at the top of the tower.
Wind electric plants must be capable of operating efficiently over a wide range of speeds, due to the wide range or variation in wind velocities used to drive the propeller or other power means of the wind electric plants. With conventional alternator exciters, it is very difficult to obtain sufficient field excitation at slow speeds without making the exciter generator relatively large in order to produce enough current for full field excitation at slow speed. However, when this is done, the exciter is considerably larger than needed at higher operating speeds, and accordingly, there is a substantial loss in propeller energy available for producing usable work. Additionally, the cost of the larger exciter generators is proportionately greater. Still further, with conventional arrangements wherein exciter generators are provided for exciting the field windings of the alternator, expensive service problems are encountered, due to the alternator and associated exciter generator being supported at the top of tall towers used in wind electric plants.
With the present invention, the conventional expensive exciter generator is eliminated, and the field windings of the alternator are excited from battery current. Thus, by utilizing direct current from a battery for exciting the field of the alternator, a relatively constant voltage is available from the battery for field excitation, and more importantly, full field excitation is easily obtained at all speeds of the alternator, including very slow speeds, and the alternator can thus produce full output at all wind velocities, including even very low wind speeds. This is a significant improvement over conventional arrangements, wherein the exciter generator has to develop considerable speed before it can fully excite the alternator field. Therefore, inasmuch as a wind electric plant must develop a full battery voltage in order to start charging the battery at slow speeds in order to utilize low wind velocities, the battery excitation system taught by applicant makes a much more ideal wind-driven alternator battery charging arrangement than any prior art arrangements known to applicant. A further important advantage of the invention is that the alternator field voltage control can be located near the batteries for easy inspection and service, rather than at the top of a tower at the alternator location. Moreover, the current drawn from the battery for field excitation is only what is needed at each speed of operation of the alternator, and since the alternator itself is considerably more efficient than the exciter generator in producing electrical energy, the alternator in the system taught by applicant can replace any battery current used in its field more efficiently from the available wind energy than can a conventional exciter, and thus the generating system of applicant is able to deliver considerably more electrical energy to the battery and to a power line or other desired use than are conventional arrangements.